The invention relates to a luminaire comprising:
concave reflectors arranged on either side of a longitudinal axis and around said longitudinal axis and each having an edge which defines a light emission window;
edge portions at least partly transverse to the longitudinal axis and transverse to the light emission window; and
connection means for accommodating a lamp to be operated, which lamp has a diameter xcfx86lamp.
Such a luminaire is known, for example, from U.S. Pat. No. 5,758,954. The known luminaire is built up from a plurality of reflectors, and the edge portions arranged transversely to the longitudinal axis are constructed as lamellae which extend between mutually opposed edges, such that the light emission window is subdivided into (separate) compartments.
The reflectors concentrate the light generated by an accommodated lamp into a beam, but they also provide a screening. The result of this is that the lamp cannot be observed from a direction perpendicular to the longitudinal axis, in so-called C0 planes, at an angle to a plane Q lying parallel to the light emission window which is smaller than a chosen cut-off angle xcex2. The cut-off angle xcex2 is usually 30xc2x0 when the position of plane Q is horizontal in the illumination of spaces in which picture screens are positioned so as to avoid a reflection of the lamp on said screens. It is the function of the lamellae to achieve that the lamp cannot be observed at angles smaller than the cut-off angle xcex2 of 30xc2x0 also from directions in the extension of the longitudinal axis, referred to as C90 planes in illumination engineering. They intercept light emitted at smaller angles and reflect, deflect, and/or scatter it. The reflectors and the lamellae have an identical function in the C planes between C0 and C90. Since there is no material which reflects incident light for 100%, but absorption always partly occurs, lamellae cause not only a screening, and thus comfort for the user of the space illuminated by the luminaire, but also a loss of light.
A disadvantage of the known luminaire is that the lamellae make the luminaire comparatively expensive. The luminaire is to be partly disassembled for the insertion or removal of a lamp, which renders the replacement of a lamp provided in the luminaire comparatively difficult. The fact that the luminaire has to be partly dismountable requires a construction of the luminaire which has the disadvantage that the assembly of the luminaire is comparatively difficult.
A luminaire is known from EP-B-0 619 006, which luminaire is built up from a plurality of reflectors. Two mutually opposed reflectors together with two edge portions, i.e. lamellae, together form a closed octagonal contour. A disadvantage of the known luminaire is that the lamellae render the luminaire comparatively expensive. It is furthermore a disadvantage that assembling of the luminaire is comparatively cumbersome, and that a lamp provided in the luminaire is difficult to replace. A further disadvantage is the loss of light caused by the lamellae.
It is an object of the invention to provide a luminaire of the kind described in the opening paragraph in which the above disadvantages are counteracted while substantially the same beam-shaping quality of light is retained.
According to the invention, this object is achieved in that a luminaire of the kind described in the opening paragraph is characterized in that the edge portions facing the longitudinal axis and arranged in mutual opposition are separated by an interspacing D measured transversely to the longitudinal axis for the purpose of inserting the lamp to be operated in the luminaire.
The above measure achieves that the luminaire can be free from lamellae, while it was found that the screening against visibility of the lamp in the planes C0-C75, for angles smaller than a cut-off angle xcex2 of 30xc2x0 to a plane Q parallel to the light emission window, and the beam-shaping qualities are substantially the same as with the known luminaire. The interspacing D is greater than xcfx86lamp for the purpose of easy mounting of the relevant lamp with diameter xcfx86lamp in the luminaire or its removal from the luminaire without the necessity of dismantling the luminaire, for example in that the edge portions are to be removed. A further advantage is that the light output of the luminaire is increased because the luminaire is free from edge portions over a distance D of at least xcfx86lamp, so that light losses owing to absorption of light by the edge portions can occur to a lesser degree. A further advantage is the low cost price of the luminaire because less material is required for the luminaire. Another advantage is that the luminaire need no longer be partly dismountable, which leads to a simplified assembly of the luminaire.
The known lamp has the further disadvantage that it may cause a glare effect which is perceived as unpleasant by an observer because a continuous reflected image of the lamp occurs in the reflector parallel to the longitudinal axis and resembling the lamp. To counteract this effect, an embodiment of the luminaire is characterized in that each reflector is concavely curved about an axis which is transverse to the light emission window. When observed from observation directions in which the angle is greater than the cut-off angle xcex2 of 30xc2x0, accordingly, the luminaire causes substantially no glare to an observer with the reflected image of the lamp.
In a favorable embodiment, the luminaire is characterized in that it is provided with screening means for screening an observer from directly emitted light originating from a lamp arranged in the luminaire. Thanks to this measure, the light beam and the lumen output remain at least substantially the same as in the known luminaire, but direct glare at angles smaller than the cut-off angle xcex2, which is also partly determined by the choice of the screening means, does not occur in planes C0-C90. The screening means may comprise, for example, a window reflector which is arranged parallel to the longitudinal axis and is situated substantially between the connection means and the light emission window. The window reflector may have a shape which is somewhat curved around the lamp so as to make this reflector rigid. A lamp provided in the luminaire can be exchanged comparatively easily because only one window reflector is to be removed from the luminaire according to the invention instead of a plurality of lamellae which are to be removed for this purpose in the known luminaire.
In an alternative embodiment in which the luminaire is provided with a lamp, the luminaire is characterized in that the screening means comprise a coating on a side of the lamp which faces towards the light emission window. The coating may be provided internally and/or externally on a portion of the circumference of the lamp and may be chosen such that the light is partly transmitted and partly reflected. If the coating is provided on the side of the lamp facing towards the light emission window over the circumference of the lamp so as to cover 140xc2x0 thereof, no glare will be visible at angles smaller than the cut-off angle xcex2 of 60xc2x0 in the planes C0-C90. The degree of light transmission of the coating can be easily adjusted through the choice of the material and/or the layer thickness of the coating. It is thus possible in a simple manner to control the brightness of the side of the lamp which faces towards the light emission window.
In an alternative embodiment, the luminaire is characterized in that the interspacing D has a value of at most 2*xcfx86lamp. If the interspacing D is smaller than 2*xcfx86lamp, the risk of glare remains comparatively small upon observation from planes other than C0 because the cut-off angle xcex2 remains at least 30 in these planes. The risk of glare may also be kept comparatively small upon observation from the planes C75-C90 in combination with the screening means.
In a favorable embodiment, the luminaire is characterized in that the interspacing D decreases in size in a direction from the light emission window to the connection means, said decrease in size having a decrease direction which encloses an angle of at least 65xc2x0 with the light emission window, preferably at least 75xc2x0. A lamp accommodated in the luminaire can be exchanged even more easily as a result of this.
In a further embodiment, the luminaire is characterized in that each reflector comprises at least two sectors which are each concavely curved around an axis which is individual to the respective sector and which is at least substantially transverse to the light emission window. The sectors of the luminaire each have a reflecting surface. The sectors are preferably characterized by cross-sections of respective C0 and C90 planes through the reflecting surface which define at least substantially the same concave curve, the respective tangent line thereto in the light emission window enclosing an angle y with the light emission window, in the plane C0 an angle xcex31 and in the plane C90 an angle xcex32, such that 90xc2x0xe2x89xa7xcex31xe2x89xa7xcex32, while xcex31xe2x89xa7xcex3xe2x89xa7xcex32 upon a traversal of the planes C0-C90, with y decreasing from xcex31 to xcex32. A C0 plane here extends through a point of the reflector surface farthest removed from the longitudinal axis, and the edge portions have ends through which a C90 plane extends. The concave curve may be defined, for example, by a parabola or a (bi-)spline function because a beam focusing of the light can be achieved comparatively easily thereby. Each reflector is built up from several sectors which may adjoin one another at an angle. This has the advantage that the reflectors may be comparatively narrow in the direction of the longitudinal axis and can be comparatively deep in a direction transverse to the longitudinal axis. The edge portions thus have a screening effect in the planes C0-C75 which is at least substantially the same as that of lamellae in the known luminaire.
In yet another embodiment, the luminaire is characterized in that the luminaire is built up from a plurality of reflectors. These reflectors may be used as separate modules, so that a flexible arrangement of the luminaire is achievable. The choice of the number and shape of the modules thus renders it possible in a simple manner to adapt the length of the luminaire to the length and shape of the lamp.
In another embodiment in which the respective light emission windows lie in one plane, the luminaire is characterized in that the plurality of reflectors are arranged in a circular shape, while the plurality of the light emission windows of the respective reflectors form one light emission window. A luminaire obtained in this manner is suitable for accommodating a circular low-pressure gas discharge lamp. It is alternatively possible through the simultaneous use of different types of reflectors in the luminaire to vary the optical properties, for example the beam focusing and the degree of diffuse reflection, of the luminaire along its longitudinal axis and to adapt them to the wishes of a customer.
The luminaire according to the invention may be designed, for example, for accommodating a straight tubular electric lamp, for example a fluorescent lamp such as a low-pressure mercury vapor discharge lamp. The luminaire may alternatively be designed for an elongate lamp which comprises, for example, two straight interconnected tubular portions next to one another. The luminaire may or may not have a housing in which the reflector is accommodated. The two mutually opposed reflectors may together form one integral part. The manufacture of the reflector may be achieved, for example, by means of deformation of, for example, metal plating, or, for example, by injection molding of, for example, synthetic resin. To obtain a suitable reflector surface quality, the reflector may be coated, for example metallized with, for example, aluminum, or, for example, may be painted with, for example, titanium oxide.